A general theory of glacier surges

D I Benn,A C Fowler,I Hewitt,H Sevestre

doi:10.1017/jog.2019.62

Abstract

AbstractWe present the first general theory of glacier surging that includes both temperate and polythermal glacier surges, based on coupled mass and enthalpy budgets. Enthalpy (in the form of thermal energy and water) is gained at the glacier bed from geothermal heating plus frictional heating (expenditure of potential energy) as a consequence of ice flow. Enthalpy losses occur by conduction and loss of meltwater from the system. Because enthalpy directly impacts flow speeds, mass and enthalpy budgets must simultaneously balance if a glacier is to maintain a steady flow. If not, glaciers undergo out-of-phase mass and enthalpy cycles, manifest as quiescent and surge phases. We illustrate the theory using a lumped element model, which parameterizes key thermodynamic and hydrological processes, including surface-to-bed drainage and distributed and channelized drainage systems. Model output exhibits many of the observed characteristics of polythermal and temperate glacier surges, including the association of surging behaviour with particular combinations of climate (precipitation, temperature), geometry (length, slope) and bed properties (hydraulic conductivity). Enthalpy balance theory explains a broad spectrum of observed surging behaviour in a single framework, and offers an answer to the wider question of why the majority of glaciers do not surge.

Highlights

Only ∼1% of the world’s glaciers have been observed to surge (Jiskoot and others, 1998; Sevestre and Benn, 2015), the interest and significance of surge-type glaciers extend far beyond their number because of the questions they raise about glacier dynamics in general
A first attempt to identify these principles was made by Sevestre and Benn (2015), who sketched the outlines of a general theory of surging based on the relationship between glacier mass and enthalpy budgets
In l and θ to explore the influence of geometry, and variations in Kto examine the influence of bed properties, as a proxy for substrate type

Summary

Introduction

Only ∼1% of the world’s glaciers have been observed to surge (Jiskoot and others, 1998; Sevestre and Benn, 2015), the interest and significance of surge-type glaciers extend far beyond their number because of the questions they raise about glacier dynamics in general. Budd, 1975; Clarke, 1976; Clarke and others, 1977; Kamb and others, 1985; Fowler, 1987a; Fowler and others, 2001) Many of these invoke specific bed types, thermal regimes or drainage system configurations, and can only explain part of the spectrum of observed surging behaviour. Global- and regional-scale analyses, show that surge-type glaciers occur within well-defined climatic envelopes, and exhibit consistent geometric characteristics regardless of the thermal regime (Clarke and others, 1986; Jiskoot and others, 2000; Sevestre and Benn, 2015). This hints that a single set of physical principles underlies all surging behaviour, irrespective of differences in detail. We compare model output with observed relationships between glacier dynamics, climate and geometry, and explore the implications of the theory for understanding the dynamic behaviour of the whole spectrum of glacier types

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Conclusion